The dehydrogenation of paraffins is an important commercial hydrocarbon conversion process because of the existing and growing demand for olefins for the manufacture of various chemical products such as detergents, high octane gasolines, and oxygenated gasoline blending components, pharmaceutical products, plastics, synthetic rubbers, and other products which are well known to those skilled in the art. One example of this process is the dehydrogenation of propane to produce propylene which can be polymerized to polypropylene, a common plastic.
Those skilled in the art of paraffin conversion processing are well versed in the production of olefins by means of catalytic dehydrogenation of paraffinic hydrocarbons. In addition, many patents have issued which teach and discuss the dehydrogenation of hydrocarbons in general. For example, U.S. Pat. No. 4,430,517 (Imai et al) discusses a dehydrogenation process and catalyst for use therein.
In existing oxidative-dehydrogenation processes for paraffin dehydrogenation, a mixture of steam and oxygen is used to combust the hydrogen partially to generate heat and increase the temperature of hydrogen and paraffin to the designed reaction temperature. The ratio of oxygen, hydrogen and paraffin needs to be controlled to avoid explosive mixture. So conventionally excess paraffins are added as diluents for dehydrogenation of paraffins. However, the addition of paraffin as diluents requires additional external heating or additional oxygen to maintain the inlet temperatures and makes the process potentially uneconomical. Alternatively, air is used instead of pure oxygen to partially combust the hydrogen. The nitrogen in the air may act as diluent to keep the mixture of oxygen, paraffin and hydrogen mixture outside the explosive unit. Still, nitrogen needs to be separated from the hydrogen rich product stream produced in the dehydrogenation reaction. The conventional separation techniques for separation of nitrogen from hydrogen are complex and require additional equipments like compressors for compression of nitrogen, contribute substantially to the operating costs. While technology has improved in the production of olefins through dehydrogenation processes, there is still room for improving the economics and the process to increase production and decrease cost.
Further, the catalysts used for the dehydrogenation of hydrocarbons are susceptible to deactivation over time. Deactivation will typically occur because of an accumulation of deposits that block active pore sites or catalytic sites on the catalyst surface. Therefore, there is a need for a new process configuration to separate nitrogen from hydrogen rich product stream produced by the dehydrogenation reaction in an economical way that can consequently enable a recycle of the separated hydrogen to the reactor to control the rate of coking on the dehydrogenation catalyst.